Both the use and radiation theory of array antennas are well known, in fact, many of the early radars developed in the late 1930s used array antennas. The frequencies of these early radars were generally VHF or lower UHF, i.e. relatively low by present day standards, and with the development of microwave radar and the application of optical techniques to microwaves, the interest in array antennas for radar applications waned in favor of reflector type antennas.
However, the array antenna has a basic advantage over other types of antennas, such as reflectors, because of the inherent ability to electronically steer the radiation pattern, or beam, without the necessity of moving mechanical structures. This basic advantage of array antennas is augmented by other advantages, such as better sidelobe control, simultaneous radiation of several patterns, higher efficiencies because of absence of spillover loss, etc.
The major disadvantages which, particularly for higher frequencies, limit the use of array antennas are the difficulty, complexity and cost of precisely controlling the phase of the energization of each of the antenna elements.
Further, conventional array antennas are not capable of simultaneously radiating multiple beams of energy in such a manner as to give to each beam a completely independent control of its frequency, position and power.
It is, therefore, an object of the present invention to provide an improved array antenna.
Another object is the provision of an improved array antenna wherein the individual elements are energized by p-n junction devices which are controlled by electron beams.
A still further object is to provide an array antenna which is capable of simultaneously radiating several microwave patterns and wherein the individual elements are energized by p-n junction devices which are controlled by electron beams that can be precisely phase, amplitude and frequency modulated.